Electrical contact brush



i E. S. MCLARN ELECTRICAL CONTACT BRUSH Filed July 29, 1944 AGENT.

March 3o, 194s.

EES/L/ENT MH rife /fu Patented Mus 3u,

y Ensc'rmcar. cou'racr nausn Ernest 8. McLarn, Manhasset, N. Y., assigner to International Standard 4Electric Corporation, New York, N. Y.. a corporation of Delaware My invention relates to electrical contact brushes and more particularly, although not exclusively, to brushes for selector switches for telecommunication systems.

An object of the invention l-s the provision oi acontact brush which when used in a telephone circuit does not give rise to microphonic noises and clicks: These noises are due largely to the movement of adjacent switches and the operation and release of associated clutch magnets. Building vibrations are' also the cause ofl clicks.

According to one feature of my invention, a contact brush comprises a pair of parallel spring members fixed to a supporting means at one end and separated at the other end by a small block of resilient material.v This block is located in the region where one of said spring members is provided with a contact surface for wipingover the contact terminals or pins. The separating block of resilient material has the eilect of damping vibration of the spring members as they stand on contact pins on terminals and eilectively preventing microphonic noises in the telephone circuit.

The above and other Iieatures will be fully understood from a reading of the following detailed description oi one embodiment oi my invention taken in conjunction with the accompanying drawings, in which:

Fig, '1 is a side elevation of a brush unit;

Fig. 2 is a section taken on the line 2-2 of Fig. 1;

Fig. 3 isa section taken on the line 3-3 of Fig. 2 showing at A and B respectively the positions o'f the brush springs when making contact with a terminal pin and when between ad jacent terminal pins.

Fig. 4 is a side elevation oi the brush guide; gig. 5 is an end elevation of the brush guide; an l Fig. 6 is a section taken on the line 6--6 of Fig. 4.

My invention is described as applied to a flattype selector switch of the kind disclosed in Patent No. 2,330,812 issued October 5, 1943, to Gerald Deakin. Only one brush unit is illustrated in the accompanying drawings but it will :"ne understood that in practice eight or any other suitable number will be mounted tothe same brush carriage which is moved'back and forth in a reciprocatory manner over the fiat terminal bank, v

Referring to Figs. 1 and 2, the brush unit is supported ,on a molded brush carriage I bytwo pins 2 which are secured in -the carriage by Anuman my 2 9, 1944, serial No. 541.172

1 claim. (ci. zoo-ies) springclips 3 which engage in grooves in the ends of the pins 2.

The brush unit comprises a punched fiber strip 4 provided with holes for the passage of vthe pins, 2 and to which are secured by rivets or eyelets 5 two outer phosphor bronze brush springs 6 and two inner brush springs 1. A

pair of depending supports 8 for a brush guide l 9 is secured at each end oi the strip 4 by an eyelet I0. The upper portions of the outer brush springs B are formed with lateral extensions II which are shaped to wipe over each side of a feederbar I2.

The lower ends of the inner brush springs 1 are formed with lateral contact surfaces adapted to wipe over the contact pins I3 in the bank, Winch pins arev made of a hard metal such as phosphor bronze or stainless steel. The inner and outer brush springs 6 and 1 are in contact for the major portion of their length but near the tip the inner brush spring 1 is bent Y at an angle to form a space between the tips as shown in Fig. 2. At this region the sides of the spring 1 are also bent back as illustrated in Fig. 3. A small block I4 of vibration-damping resilient material,.such as Neoprene, is positioned in the space between the tips of each pair of brush springs 6, 1 and is held in position by a lip I5 on the lower edge of the spring 6 and by the bent back sides oi the spring 1. Oscillograph tests have shown that the block of soft material III eiiectively damps vibration of the brushes, prevents vibration of the springs and reduces microphonic contact between the brushes and the terminal pins I3.

Figs. 4, 5 and 6 show the construction of the brush guide 9 which comprises a molded Bakelite block formed with two slots I6 to accommodate inturnedv ends of the supports 8. At the center at its lower edges as shown yin Fig. 6. The ends of the slot I9 are also ared as shown inyFig. 5 in order to guide the pins into the slot. The guide assures alignment of the, brushes with the pins I3 and the accurate making and breaking ot the contact. It prevents one brush from pro- Jecting further between adjacent pins than the 3 other and thus allows of maximum rubbing coutI tact by each brush which in practice is about 85% of the distance between pin centers.

It will be understood that while I have chosen to illustrate my invention as applied to a attype selector switch, it is applicable to many other types of switch Without departing from the scope of the invention as dened by the appended claim. i

I claim:

A contact brush for use in apparatus wherein contact and alignment are eected in succession between the contact brush and a plurality of linearly mounted contact pins, said contact brush comprising a first pair of substantially parallel 1 metallic spring members having inner contact surfaces at one end of each for making electrical contact with said contact pins, supporting means for said spring members, a second pair of substantially parallel springr members mounted on said supporting means one behind each of the iirst pair of spring members and vibraateatro` tion-damping blocks of homogeneous structure mounted one between and supported solely by each two adjacent spring members of said rst and second pairs oi spring members.

ERNEST S. MCLARN.

REFERENCES CITED The followingreferences are of record in the ille of this patent: Y

' UNITED STATES PATENTS Great Britain Sept. 15, 1921 

